Clavulanate-selective electrodes - application to pharmaceutical formulations

The construction and assessment of a clavulanate anion-selective electrode and its application to the analysis of pharmaceutical formulations by direct potentiometry are described. The electrode, prepared without inner reference solution, was fabricated by use of a PVC membrane, with bis(triphenyl-phosphoranylidene)ammonium clavulanate as ion-exchanger dissolved in 2-nitrophenyl octyl ether as intermediate solvent and p-t-octylphenol as additive. The response of the electrode was linearly dependent on concentration within the range 2.4 x 10(-3)-1 x 10(-1) mol dm(-3) (ionic strength adjusted to 0.1 mol dm(-3)); the slope of the calibration plot was -59.4+/-0.9 mV decade(-1) and the reproducibility +/-0.6 mV day(-1). The response time was less than 20 s. Relative errors were <3.5% when results from analysis by direct potentiometry were compared with those from the reference method.